Essential knowledge for wire and cable inspection - Low-temperature winding test

I. Inspection Purpose

Low-temperature winding test is a method for assessing the cold resistance of wires and cables, and it is used to test whether wire and cable products can operate normally in extremely cold regions or other low-temperature conditions. The cold resistance performance of the product, in the case of fixed installation, requires that the insulation and sheath of the product do not crack when installed under the minimum allowable ambient temperature and the minimum installation bending radius, and that it does not crack under the action of bending prestress or molecular structural force during long-term operation in low-temperature conditions. For products used in mobile or semi-mobile applications, it is required that they can withstand mechanical stress from multiple bends with smaller bending radii at low temperatures without damaging the insulation and sheath. That is, the insulation and sheath of the product should still maintain a certain degree of flexibility and elasticity under low-temperature conditions. Therefore, the purpose of the low-temperature winding test is to assess whether the low-temperature bending performance of the product meets the requirements stipulated in the standard.

Ii. Scope of Application

This test is applicable to circular insulated wire cores with an outer diameter of 12.5mm or less and fan-shaped insulated wire cores where dumbbell specimens cannot be prepared.

2. This test is applicable to sheathed cables with an outer diameter of 12.5mm or less and flat cables with short shaft dimensions of 20mm or less.

Iii. Inspection Basis

GB/T 2951.14-2008 /IEC 60811-1-4:2001 and related product standards.

Iv. Test Equipment and Apparatus

Low-temperature chamber, low-temperature winding device.

V. Sampling and Testing Equipment

Take two samples of appropriate length from each test cable.

2. The outer sheath of the insulating low-temperature winding specimens should be removed (if there is an outer sheath).

3. For low-temperature winding samples with sheaths, all protective layers on the sheaths should be removed.

Vi. Test Procedures

Select the test temperature.

a. Polyvinyl chloride insulated cable: 15±2℃

b. Rubber insulated cable: 35±2℃

c. Or as stipulated by relevant standards.

2. Select the diameter of the test bar.

For circular insulated core and sheathed cables, the diameter of the test rod should be 4 to 5 times that of the sample.

b. The diameter of the test bar for the fan-shaped specimen should be 4 to 5 times the size of the short axis.

c. The diameter of the test bar for flat flexible wire should be 4 to 5 times the size of the short axis of the sample. When winding, the short axis should be perpendicular to the test bar.

3. Fix one end of the sample on the winding device. The equipment containing the sample should be placed in a low-temperature box at the specified temperature for no less than 16 hours. The 16-hour cooling time includes the time required for cooling the equipment.

4. If the test equipment has been pre-cooled, as long as the sample reaches the specified test temperature. Then the cooling time can be shortened, but it must not be less than 4 hours. If both the test equipment and the samples have been cooled, each sample should be fixed on the test equipment and cooled for 1 hour.

Outer diameter of the sample (mm

Number of rotations n

d ≤2.5

10

2.5 < d 4.5 or less

6

4.5 < d 6.5 or less

4

6.5 < d 8.5 or less

3

8.5 < d

2

After the specified cooling time is over, the test bar should be rotated at a constant speed of approximately one turn every 5 seconds (the number of turns is specified in the above table), and the sample should be neatly wound into a tight helix on the test bar. If the sample is fan-shaped, the circular "back" of the sample should be in contact with the test rod, and then the sample should be held on the test rod to restore it to a temperature close to the ambient temperature.

Vii. Evaluation of Test Results

After the test is completed as per the regulations, inspect the samples still on the test rods. When inspected with normal vision or corrected vision without a magnifying glass, both insulating samples should be free of any cracks to be considered qualified.